Hi WalterI cannot reproduce your problem either, all of your arc`s and other entities on layer 'Schnitt' can be lengthened by your value of I unit (1 cm).Which two arcs are in question here?Is it possible for you to highlight the two arcs and submit another drawing?

Hmm, above condition will not cover my problem... An Amount of 12 or 13 will satisfy the condition (length > arc circumference) but would have lengthened the arc!

r=1.8 –> circumference ca. 11.3.. Try series 1, 2, ... 9 for Amount:1..5 lengthen icreases6..9 lengthen decreases10..11 no lenthen12.. lengthen icreases arc againAs the behavior is different for the 2 arcs, obviously the length and/or geometry of the already existing arc is part of the calculation too...

Conclusion:I think the algorithm how much the arc gets lengthened should be modified. Proposal: Amount is only the prolongation of the arc (= how much longer the arc becomes). ⇒ Same behavior as lengthen of a line. The maximum prolongation is Pi x r regardless of how huge Amount is set.

As there is a preview the user can abort and change Amount, if the result is not what he likes it to be. This will be much more handsome than a message that the result will be invalid.